Method for impregnating fiber rovings

ABSTRACT

A die and method for impregnating at least one fiber roving with a polymer resin are disclosed. The die includes an impregnation section. The impregnation section includes an impregnation zone configured to impregnate the roving with the resin. The impregnation zone includes a plurality of contact surfaces. At least one of the plurality of contact surfaces is configured such that a normal force of the roving is less than or equal to a lift force of the resin at an impregnation location on the contact surface during impregnation of the roving with the resin by the contact surface.

This application is a divisional of U.S. patent application Ser. No.13/707,673, filed on Dec. 7, 2012, titled: “SYSTEM AND METHOD FORIMPREGNATING FIBER ROVINGS”, which claims priority to U.S. ProvisionalPatent Application Ser. No. 61/569,055, filed Dec. 9, 2011, titled: “DIEAND METHOD FOR IMPREGNATING FIBER ROVINGS”, both of which are herebyincorporated by reference in their entireties.

BACKGROUND OF THE INVENTION

Fiber rovings have been employed in a wide variety of applications. Forexample, such rovings have been utilized to form fiber-reinforcedcomposite rods. The rods may be utilized as lightweight structuralreinforcements. For example, power umbilicals are often used in thetransmission of fluids and/or electric signals between the sea surfaceand equipment located on the sea bed. To help strengthen suchumbilicals, attempts have been made to use pultruded carbon fiber rodsas separate load carrying elements.

Another application that is particularly suited for the use of fiberrovings is in the formation of profiles. Profiles are pultruded partswith a wide variety of cross-sectional shapes, and may be employed as astructural member for window lineals, decking planks, railings,balusters, roofing tiles, siding, trim boards, pipe, fencing, posts,light posts, highway signage, roadside marker posts, etc. Hollowprofiles have been formed by pulling (“pultruding”) continuous fiberrovings through a resin and then shaping the fiber-reinforced resinwithin a pultrusion die.

Further, fiber rovings may generally be utilized in any suitableapplications to form, for example, suitable fiber reinforced plastics.As is generally known in the art, rovings utilized in these applicationsare typically combined with a polymer resin.

There are many significant problems, however, with currently knownrovings and the resulting applications that utilize such rovings. Forexample, many rovings rely upon thermoset resins (e.g., vinyl esters) tohelp achieve desired strength properties. Thermoset resins are difficultto use during manufacturing and do not possess good bondingcharacteristics for forming layers with other materials. Further,attempts have been made to form rovings from thermoplastic polymers inother types of applications. U.S. Patent Publication No. 2005/0186410 toBryant, et al., for instance, describes attempts that were made to embedcarbon fibers into a thermoplastic resin to form a composite core of anelectrical transmission cable. Unfortunately, Bryant, et al. notes thatthese cores exhibited flaws and dry spots due to inadequate wetting ofthe fibers, which resulted in poor durability and strength. Anotherproblem with such cores is that the thermoplastic resins could notoperate at a high temperature.

As such, a need currently exists for an improved die and method forimpregnating a fiber roving. Specifically, a need currently exists for adie and method that produce fiber rovings which provide the desiredstrength, durability, and temperature performance demanded by aparticular application.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a die forimpregnating at least one fiber roving with a polymer resin isdisclosed. The die includes an impregnation section. The impregnationsection includes an impregnation zone configured to impregnate theroving with the resin. The impregnation zone includes a plurality ofcontact surfaces. At least one of the plurality of contact surfaces isconfigured such that a normal force of the roving is less than or equalto a lift force of the resin at an impregnation location on the contactsurface during impregnation of the roving with the resin by the contactsurface.

In accordance with another embodiment of the present invention, a methodfor impregnating at least one fiber roving with a polymer resin isdisclosed. The method includes flowing a polymer resin through amanifold assembly of a die, the manifold assembly including a pluralityof branched runners, and coating at least one fiber roving with theresin. The method further includes traversing the coated roving throughan impregnation zone of the die to impregnate the roving with the resin,the impregnation zone including a plurality of contact surfaces. Atleast one of the plurality of contact surfaces is configured such that anormal force of the roving is less than or equal to a lift force of theresin at an impregnation location on the contact surface duringimpregnation of the roving with the resin by the contact surface.

Other features and aspects of the present invention are set forth ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof to one skilled in the art, is set forth moreparticularly in the remainder of the specification, including referenceto the accompanying figures, in which:

FIG. 1 is a schematic illustration of one embodiment of an impregnationsystem for use in the present invention;

FIG. 2 is a perspective view of one embodiment of a die for use in thepresent invention;

FIG. 3 is an opposing perspective view of one embodiment of a die foruse in the present invention;

FIG. 4 is a cross-sectional view of the die shown in FIG. 2;

FIG. 5 is an exploded view of one embodiment of a manifold assembly andgate passage for a die that may be employed in the present invention;

FIG. 6 is a plan view of one embodiment of a manifold assembly that maybe employed in the present invention;

FIG. 7 is a plan view of another embodiment of a manifold assembly thatmay be employed in the present invention;

FIG. 8 is a plan view of another embodiment of a manifold assembly thatmay be employed in the present invention;

FIG. 9 is a plan view of another embodiment of a manifold assembly thatmay be employed in the present invention;

FIG. 10 is a plan view of another embodiment of a manifold assembly thatmay be employed in the present invention;

FIG. 11 is a plan view of another embodiment of a manifold assembly thatmay be employed in the present invention;

FIG. 12 is a perspective view of one embodiment of a second impregnationplate at least partially defining an impregnation zone that may beemployed in the present invention;

FIG. 13 is a close-up cross-sectional view, as indicated in FIG. 4, ofone embodiment of a portion of an impregnation zone that may be employedin the present invention;

FIG. 14 is a close-up cross-sectional view of another embodiment of aportion of an impregnation zone that may be employed in the presentinvention;

FIG. 15 is a close-up cross-sectional view of another embodiment of aportion of an impregnation zone that may be employed in the presentinvention;

FIG. 16 is a close-up cross-sectional view of another embodiment of aportion of an impregnation zone that may be employed in the presentinvention;

FIG. 17 is a close-up cross-sectional view of another embodiment of aportion of an impregnation zone that may be employed in the presentinvention;

FIG. 18 is a close-up cross-sectional view, as indicated in FIG. 4, ofone embodiment of a downstream end portion of an impregnation zone thatmay be employed in the present invention;

FIG. 19 is one embodiment of a geometric representation of a rovingtraversing a contact surface that may be utilized to calculate a normalforce of the roving according to the present invention;

FIG. 20 is one embodiment of a geometric representation of theinteraction between a roving, resin, and a contact surface that may beutilized to calculate a lift force of the resin according to the presentinvention;

FIG. 21 is a perspective view of one embodiment of a land zone that maybe employed in the present invention;

FIG. 22 is a perspective view of another embodiment of a land zone thatmay be employed in the present invention;

FIG. 23 is a perspective view of one embodiment of a consolidated ribbonfor use in the present invention; and

FIG. 24 is a cross-sectional view of another embodiment of aconsolidated ribbon for use in the present invention.

Repeat use of reference characters in the present specification anddrawings is intended to represent the same or analogous features orelements of the present invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention.

Generally speaking, the present invention is directed to a die andmethod for impregnating fiber rovings with a polymer resin. Theimpregnated fiber rovings may be utilized in composite rods, profiles,or any other suitable fiber reinforced plastic applications. The dieaccording to the present invention generally includes a manifoldassembly, an impregnation zone at least partially defined in animpregnation section, and a gate passage therebetween. The manifoldassembly distributes a polymer resin therethrough. Upon exiting themanifold assembly, the resin flows into and through the gate passage.The rovings are traversed through the die such that the resin, uponexiting the gate passage, coats the rovings. After being coated with theresin, the rovings are traversed through the impregnation zone andimpregnated therein with the resin.

According to further aspects of the present invention, an extrusiondevice may be employed in conjunction with the die to impregnate therovings with the polymer. Among other things, the extrusion devicefurther facilitates the ability of the polymer to be applied to theentire surface of the fibers, as discussed below.

Referring to FIG. 1, one embodiment of such an extrusion device isshown. More particularly, the apparatus includes an extruder 120containing a screw shaft 124 mounted inside a barrel 122. A heater 130(e.g., electrical resistance heater) is mounted outside the barrel 122.During use, a polymer feedstock 127 is supplied to the extruder 120through a hopper 126. The feedstock 127 is conveyed inside the barrel122 by the screw shaft 124 and heated by frictional forces inside thebarrel 122 and by the heater 130. Upon being heated, the feedstock 127exits the barrel 122 through a barrel flange 128 and enters a die flange132 of an impregnation die 150.

A continuous fiber roving 142 or a plurality of continuous fiber rovings142 are supplied from a reel or reels 144 to die 150. The rovings 142are generally positioned side-by-side, with minimal to no distancebetween neighboring rovings, before impregnation. The feedstock 127 mayfurther be heated inside the die by heaters 133 mounted in or around thedie 150. The die is generally operated at temperatures that aresufficient to cause and/or maintain the proper melt temperature for thepolymer, thus allowing for the desired level of impregnation of therovings by the polymer. Typically, the operation temperature of the dieis higher than the melt temperature of the polymer, such as attemperatures from about 200° C. to about 450° C. When processed in thismanner, the continuous fiber rovings 142 become embedded in the polymermatrix, which may be a resin 214 (FIG. 4) processed from the feedstock127. The mixture may then exit the impregnation die 150 as wettedcomposite or extrudate 152.

As used herein, the term “roving” generally refers to a bundle ofindividual fibers 300. The fibers 300 contained within the roving can betwisted or can be straight. The rovings may contain a single fiber typeor different types of fibers 300. Different fibers may also be containedin individual rovings or, alternatively, each roving may contain adifferent fiber type. The continuous fibers employed in the rovingspossess a high degree of tensile strength relative to their mass. Forexample, the ultimate tensile strength of the fibers is typically fromabout 1,000 to about 15,000 Megapascals (“MPa”), in some embodimentsfrom about 2,000 MPa to about 10,000 MPa, and in some embodiments, fromabout 3,000 MPa to about 6,000 MPa. Such tensile strengths may beachieved even though the fibers are of a relatively light weight, suchas a mass per unit length of from about 0.05 to about 2 grams per meter,in some embodiments from about 0.4 to about 1.5 grams per meter. Theratio of tensile strength to mass per unit length may thus be about1,000 Megapascals per gram per meter (“MPa/g/m”) or greater, in someembodiments about 4,000 MPa/g/m or greater, and in some embodiments,from about 5,500 to about 20,000 MPa/g/m. Such high strength fibers may,for instance, be metal fibers, glass fibers (e.g., E-glass, A-glass,C-glass, D-glass, AR-glass, R-glass, S1-glass, S2-glass, etc.), carbonfibers (e.g., amorphous carbon, graphitic carbon, or metal-coatedcarbon, etc.), boron fibers, ceramic fibers (e.g., alumina or silica),aramid fibers (e.g., Kevlar® marketed by E. I. duPont de Nemours,Wilmington, Del.), synthetic organic fibers (e.g., polyamide,polyethylene, paraphenylene, terephthalamide, polyethylene terephthalateand polyphenylene sulfide), and various other natural or syntheticinorganic or organic fibrous materials known for reinforcingthermoplastic and/or thermoset compositions. Carbon fibers areparticularly suitable for use as the continuous fibers, which typicallyhave a tensile strength to mass ratio in the range of from about 5,000to about 7,000 MPa/g/m. The continuous fibers often have a nominaldiameter of about 4 to about 35 micrometers, and in some embodiments,from about 9 to about 35 micrometers. The number of fibers contained ineach roving can be constant or vary from roving to roving. Typically, aroving contains from about 1,000 fibers to about 50,000 individualfibers, and in some embodiments, from about 5,000 to about 30,000fibers.

Any of a variety of thermoplastic or thermoset polymers may be employedto form the polymer matrix in which the continuous fibers are embedded.For example, suitable thermoplastic polymers for use in the presentinvention may include, for instance, polyolefins (e.g., polypropylene,propylene-ethylene copolymers, etc.), polyesters (e.g., polybutyleneterephalate (“PBT”)), polycarbonates, polyamides (e.g., Nylon™),polyether ketones (e.g., polyetherether ketone (“PEEK”)),polyetherimides, polyarylene ketones (e.g., polyphenylene diketone(“PPDK”)), liquid crystal polymers, polyarylene sulfides (e.g.,polyphenylene sulfide (“PPS”), poly(biphenylene sulfide ketone),poly(phenylene sulfide diketone), poly(biphenylene sulfide), etc.),fluoropolymers (e.g., polytetrafluoroethylene-perfluoromethylvinyletherpolymer, perfluoro-alkoxyalkane polymer, petrafluoroethylene polymer,ethylene-tetrafluoroethylene polymer, etc.), polyacetals, polyurethanes,polycarbonates, styrenic polymers (e.g., acrylonitrile butadiene styrene(“ABS”)), and so forth.

The properties of the polymer matrix are generally selected to achievethe desired combination of processability and performance. For example,the melt viscosity of the polymer matrix is generally low enough so thatthe polymer can adequately impregnate the fibers. In this regard, themelt viscosity typically ranges from about 25 to about 1,000Pascal-seconds (“Pa-s”), in some embodiments from 50 about 500 Pa-s, andin some embodiments, from about 60 to about 200 Pa-s, determined at theoperating conditions used for the polymer (e.g., about 360° C.).Likewise, when the impregnated rovings are intended for applicationsinvolving high temperatures (e.g., high voltage transmission cables), apolymer is employed that has a relatively high melting temperature. Forexample, the melting temperature of such high temperature polymers mayrange from about 200° C. to about 500° C., in some embodiments fromabout 225° C. to about 400° C., and in some embodiments, from about 250°C. to about 350° C.

Polyarylene sulfides are particularly suitable for use in the presentinvention as a high temperature matrix with the desired melt viscosity.Polyphenylene sulfide, for example, is a semi-crystalline resin thatgenerally includes repeating monomeric units represented by thefollowing general formula:

These monomeric units typically constitute at least 80 mole %, and insome embodiments, at least 90 mole %, of the recurring units, in thepolymer. It should be understood, however, the polyphenylene sulfide maycontain additional recurring units, such as described in U.S. Pat. No.5,075,381 to Gotoh, et al., which is incorporated herein in its entiretyby reference thereto for all purposes. When employed, such additionalrecurring units typically constitute no more than about 20 mole % of thepolymer. Commercially available high melt viscosity polyphenylenesulfides may include those available from Ticona LLC (Florence, Ky.)under the trade designation FORTRON®. Such polymers may have a meltingtemperature of about 285° C. (determined according to ISO 11357-1,2,3)and a melt viscosity of from about 260 to about 320 Pascal-seconds at310° C.

A pressure sensor 137 (FIGS. 2 and 3) may sense the pressure near theimpregnation die 150 to allow control to be exerted over the rate ofextrusion by controlling the rotational speed of the screw shaft 124, orthe feed rate of the feeder. That is, the pressure sensor 137 ispositioned near the impregnation die 150, such as upstream of themanifold assembly 220, so that the extruder 120 can be operated todeliver a correct amount of resin 214 for interaction with the fiberrovings 142. After leaving the impregnation die 150, the extrudate 152,or impregnated fiber rovings 142, may enter an optional pre-shaping orguiding section (not shown) before entering a nip formed between twoadjacent rollers 190. Although optional, the rollers 190 can help toconsolidate the extrudate 152 into the form of a ribbon, as well asenhance fiber impregnation and squeeze out any excess voids. In additionto the rollers 190, other shaping devices may also be employed, such asa die system. Regardless, the resulting consolidated ribbon 156 ispulled by tracks 162 and 164 mounted on rollers. The tracks 162 and 164also pull the extrudate 152 from the impregnation die 150 and throughthe rollers 190. If desired, the consolidated ribbon 156 may be wound upat a section 171. Generally speaking, the resulting ribbons arerelatively thin and typically have a thickness of from about 0.05 toabout 1 millimeter, in some embodiments from about 0.1 to about 0.8millimeters, and in some embodiments, from about 0.2 to about 0.4millimeters.

Perspective views of one embodiment of a die 150 according to thepresent disclosure are further shown in FIGS. 2 and 3. As shown, resin214 is flowed into the die 150 as indicated by resin flow direction 244.The resin 214 is distributed within the die 150 and then interacted withthe rovings 142. The rovings 142 are traversed through the die 150 inroving run direction 282, and are coated with resin 214. The rovings 142are then impregnated with the resin 214, and these impregnated rovings142 exit the die 150.

Within the impregnation die, it is generally desired that the rovings142 are traversed through an impregnation zone 250 to impregnate therovings with the polymer resin 214. In the impregnation zone 250, thepolymer resin may be forced generally transversely through the rovingsby shear and pressure created in the impregnation zone 250, whichsignificantly enhances the degree of impregnation. This is particularlyuseful when forming a composite from ribbons of a high fiber content,such as about 35% weight fraction (“Wf”) or more, and in someembodiments, from about 40% Wf or more. Typically, the die 150 willinclude a plurality of contact surfaces 252, such as for example atleast 2, at least 3, from 4 to 7, from 2 to 20, from 2 to 30, from 2 to40, from 2 to 50, or more contact surfaces 252, to create a sufficientdegree of penetration and pressure on the rovings 142. Although theirparticular form may vary, the contact surfaces 252 typically possess acurvilinear surface, such as a curved lobe, pin, etc. The contactsurfaces 252 are also typically made of a metal material.

FIG. 4 shows a cross-sectional view of an impregnation die 150. Asshown, the impregnation die 150 includes a manifold assembly 220 and animpregnation section. The impregnation section includes an impregnationzone 250. In some embodiments, the impregnation section additionallyincludes a gate passage 270. The manifold assembly 220 is provided forflowing the polymer resin 214 therethrough. For example, the manifoldassembly 220 may include a channel 222 or a plurality of channels 222.The resin 214 provided to the impregnation die 150 may flow through thechannels 222.

As shown in FIGS. 5 through 11, in exemplary embodiments, at least aportion of each of the channels 222 may be curvilinear. The curvilinearportions may allow for relatively smooth redirection of the resin 214 invarious directions to distribute the resin 214 through the manifoldassembly 220, and may allow for relatively smooth flow of the resin 214through the channels 222. Alternatively, the channels 222 may be linear,and redirection of the resin 214 may be through relatively sharptransition areas between linear portions of the channels 222. It shouldfurther be understood that the channels 222 may have any suitable shape,size, and/or contour.

The plurality of channels 222 may, in exemplary embodiments as shown inFIGS. 5 through 11, be a plurality of branched runners 222. The runners222 may include a first branched runner group 232. The first branchedrunner group 232 includes a plurality of runners 222 branching off froman initial channel or channels 222 that provide the resin 214 to themanifold assembly 220. The first branched runner group 232 may include2, 3, 4 or more runners 222 branching off from the initial channels 222.

If desired, the runners 222 may include a second branched runner group234 diverging from the first branched runner group 232, as shown inFIGS. 5 and 7 through 11. For example, a plurality of runners 222 fromthe second branched runner group 234 may branch off from one or more ofthe runners 222 in the first branched runner group 232. The secondbranched runner group 234 may include 2, 3, 4 or more runners 222branching off from runners 222 in the first branched runner group 232.

If desired, the runners 222 may include a third branched runner group236 diverging from the second branched runner group 234, as shown inFIGS. 5 and 8 through 9. For example, a plurality of runners 222 fromthe third branched runner group 236 may branch off from one or more ofthe runners 222 in the second branched runner group 234. The thirdbranched runner group 236 may include 2, 3, 4 or more runners 222branching off from runners 222 in the second branched runner group 234.

In some exemplary embodiments, as shown in FIGS. 5 through 11, theplurality of branched runners 222 have a symmetrical orientation along acentral axis 224. The branched runners 222 and the symmetricalorientation thereof generally evenly distribute the resin 214, such thatthe flow of resin 214 exiting the manifold assembly 220 and coating therovings 142 is substantially uniformly distributed on the rovings 142.This desirably allows for generally uniform impregnation of the rovings142.

Further, the manifold assembly 220 may in some embodiments define anoutlet region 242. The outlet region 242 is that portion of the manifoldassembly 220 wherein resin 214 exits the manifold assembly 220. Thus,the outlet region 242 generally encompasses at least a downstreamportion of the channels or runners 222 from which the resin 214 exits.In some embodiments, as shown in FIGS. 5 through 10, at least a portionof the channels or runners 222 disposed in the outlet region 242 have anincreasing area in a flow direction 244 of the resin 214. The increasingarea allows for diffusion and further distribution of the resin 214 asthe resin 214 flows through the manifold assembly 220, which furtherallows for substantially uniform distribution of the resin 214 on therovings 142. Additionally or alternatively, various channels or runners222 disposed in the outlet region 242 may have constant areas in theflow direction 244 of the resin 214, as shown in FIG. 11, or may havedecreasing areas in the flow direction 244 of the resin 214.

In some embodiments, as shown in FIGS. 5 through 9, each of the channelsor runners 222 disposed in the outlet region 242 is positioned such thatresin 214 flowing therefrom is combined with resin 214 from otherchannels or runners 222 disposed in the outlet region 242. Thiscombination of the resin 214 from the various channels or runners 222disposed in the outlet region 242 produces a generally singular anduniformly distributed flow of resin 214 from the manifold assembly 220to substantially uniformly coat the rovings 142. Alternatively, as shownin FIGS. 10 and 11, various of the channels or runners 222 disposed inthe outlet region 242 may be positioned such that resin 214 flowingtherefrom is discrete from the resin 214 from other channels or runners222 disposed in the outlet region 242. In these embodiments, a pluralityof discrete but generally evenly distributed resin flows 214 may beproduced by the manifold assembly 220 for substantially uniformlycoating the rovings 142.

As shown in FIG. 4, at least a portion of the channels or runners 222disposed in the outlet region 242 have curvilinear cross-sectionalprofiles. These curvilinear profiles allow for the resin 214 to begradually directed from the channels or runners 222 generally downwardtowards the rovings 142. Alternatively, however, these channels orrunners 222 may have any suitable cross-sectional profiles.

As further illustrated in FIGS. 4 and 5, after flowing through themanifold assembly 220, the resin 214 may flow through gate passage 270.Gate passage 270 is positioned between the manifold assembly 220 and theimpregnation zone 250, and is provided for flowing the resin 214 fromthe manifold assembly 220 such that the resin 214 coats the rovings 142.Thus, resin 214 exiting the manifold assembly 220, such as throughoutlet region 242, may enter gate passage 270 and flow therethrough.

In some embodiments, as shown in FIG. 4, the gate passage 270 extendsvertically between the manifold assembly 220 and the impregnation zone250. Alternatively, however, the gate passage 270 may extend at anysuitable angle between vertical and horizontal such that resin 214 isallowed to flow therethrough.

Further, as shown in FIG. 4, in some embodiments at least a portion ofthe gate passage 270 has a decreasing cross-sectional profile in theflow direction 244 of the resin 214. This taper of at least a portion ofthe gate passage 270 may increase the flow rate of the resin 214 flowingtherethrough before it contacts the rovings 142, which may allow theresin 214 to impinge on the rovings 142. Initial impingement of therovings 142 by the resin 214 provides for further impregnation of therovings, as discussed below. Further, tapering of at least a portion ofthe gate passage 270 may increase backpressure in the gate passage 270and the manifold assembly 220, which may further provide more even,uniform distribution of the resin 214 to coat the rovings 142.Alternatively, the gate passage 270 may have an increasing or generallyconstant cross-sectional profile, as desired or required.

Upon exiting the manifold assembly 220 and the gate passage 270 of thedie 150 as shown in FIG. 4, the resin 214 contacts the rovings 142 beingtraversed through the die 150. As discussed above, the resin 214 maysubstantially uniformly coat the rovings 142, due to distribution of theresin 214 in the manifold assembly 220 and the gate passage 270.Further, in some embodiments, the resin 214 may impinge on an uppersurface of each of the rovings 142, or on a lower surface of each of therovings 142, or on both an upper and lower surface of each of therovings 142. Initial impingement on the rovings 142 provides for furtherimpregnation of the rovings 142 with the resin 214. Impingement on therovings 142 may be facilitated by the velocity of the resin 214 when itimpacts the rovings 142, the proximity of the rovings 142 to the resin214 when the resin exits the manifold assembly 220 or gate passage 270,or other various variables.

As shown in FIG. 4, the coated rovings 142 are traversed in rundirection 282 through impregnation zone 250. The impregnation zone 250is in fluid communication with the manifold assembly 220, such asthrough the gate passage 270 disposed therebetween. The impregnationzone 250 is configured to impregnate the rovings 142 with the resin 214.

For example, as discussed above, in exemplary embodiments as shown inFIGS. 4 and 12 through 18, the impregnation zone 250 includes aplurality of contact surfaces 252. The rovings 142 are traversed overthe contact surfaces 252 in the impregnation zone. Impingement of therovings 142 on the contact surface 252 creates shear and pressuresufficient to impregnate the rovings 142 with the resin 214 coating therovings 142.

In some embodiments, as shown in FIG. 4, the impregnation zone 250 isdefined between two spaced apart opposing impregnation plates 256 and258, which may be included in the impregnation section. First plate 256defines a first inner surface 257, while second plate 258 defines asecond inner surface 259. The impregnation zone 250 is defined betweenthe first plate 256 and the second plate 258. The contact surfaces 252may be defined on or extend from both the first and second innersurfaces 257 and 259, or only one of the first and second inner surfaces257 and 259.

In exemplary embodiments, as shown in FIGS. 4, 13, and 15 through 18,the contact surfaces 252 may be defined alternately on the first andsecond surfaces 257 and 259 such that the rovings alternately impinge oncontact surfaces 252 on the first and second surfaces 257 and 259. Thus,the rovings 142 may pass contact surfaces 252 in a waveform, tortuous orsinusoidual-type pathway, which enhances shear.

Angle 254 at which the rovings 142 traverse the contact surfaces 252 maybe generally high enough to enhance shear and pressure, but not so highto cause excessive forces that will break the fibers. Thus, for example,the angle 254 may be in the range between approximately 1° andapproximately 30°, and in some embodiments, between approximately 5° andapproximately 25°.

As stated above, contact surfaces 252 typically possess a curvilinearsurface, such as a curved lobe, pin, etc. In exemplary embodiments asshown, a plurality of peaks, which may form contact surfaces 252, andvalleys are thus defined. Further, in many exemplary embodiments, theimpregnation zone 250 has a waveform cross-sectional profile. In oneexemplary embodiment as shown in FIGS. 4, 13, and 18, the contactsurfaces 252 are lobes that form portions of the waveform surfaces ofboth the first and second plates 256 and 258 and define the waveformcross-sectional profile. FIG. 12 illustrates the second plate 258 andthe various contact surfaces thereon that form at least a portion of theimpregnation zone 250 according to some of these embodiments.

In other embodiments, as shown in FIG. 14, the contact surfaces 252 arelobes that form portions of a waveform surface of only one of the firstor second plate 256 or 258. In these embodiments, impingement occursonly on the contact surfaces 252 on the surface of the one plate. Theother plate may generally be flat or otherwise shaped such that nointeraction with the coated rovings occurs.

In other alternative embodiments, as shown in FIGS. 15 through 17, theimpregnation zone 250 may include a plurality of pins (or rods) 260,each pin having a contact surface 252. The pins 260 may be static, asshown in FIGS. 15 and 16, freely rotational (not shown), or rotationallydriven, as shown in FIG. 17. Further, the pins 260 may be mounteddirectly to the surface of the plates defining the impingement zone, asshown in FIG. 15, or may be spaced from the surface as shown in FIGS. 16and 17. It should be noted that the pins 260 may be heated by heaters133, or may be heated individually or otherwise as desired or required.Further, the pins 260 may be contained within the die 150, or may extendoutwardly from the die 150 and not be fully encased therein.

In further alternative embodiments, the contact surfaces 252 andimpregnation zone 250 may comprise any suitable shapes and/or structuresfor impregnating the rovings 142 with the resin 214 as desired orrequired.

As discussed, a roving 142 traversed through an impregnation zone 250according to the present disclosure may become impregnated by resin 214,thus resulting in an impregnated roving 142 exiting the impregnationzone 250, such as downstream of the contact surfaces 252 in the rundirection 282. Further, in exemplary embodiments of the presentdisclosure, such impregnated roving 142 may desirably be generallyuniform. A uniform impregnated roving 142 may have fibers 300 generallyor approximately uniformly distributed therein, and/or may have agenerally uniform coating of resin 214 surrounding those fibers. Thus, agenerally uniform impregnated roving 142 may have a cross-section, asshown in FIG. 24 and discussed below, with a generally uniformdistribution of fibers and resin 214. Such uniform impregnated roving142 may have a number of different advantages. For example, a uniformimpregnated roving 142 may provide improved strength characteristics.

To facilitate the production of uniform impregnated rovings 142according to the present disclosure, one or more contact surfaces 252may have various characteristics that adjust the various forces appliedto and by the rovings 142 and resin 214 during impregnation. Forexample, FIGS. 4 and 18 illustrate embodiments of an impregnationsection and impregnation zone 250 for impregnated a roving 142 with aresin 214. As shown, one or more contact surfaces, designated as contactsurfaces 253 for purposes of the present disclosure, may be configuredsuch that a normal force of one or more rovings 142 traversing thatcontact surface 253 is less than or equal to a lift force, such as ahydraulic lift force, of the associated resin 214 on that roving 142during impregnation of the roving 142 with the resin 214 by the contactsurface 253. Typical dies 150 and impregnation sections include contactsurfaces that cause rovings 142 traversing those contact surfaces tohave normal forces that are greater than the lift forces of theassociated resin 214. However, this typical arrangement of the contactsurfaces may cause excess resin 214 to be removed from the rovings 142during impregnation and/or may cause resin 214 to migrate to the oneside of the rovings 142, and may cause contact between the rovings 142and the contact surfaces when the rovings are traversing the contactsurfaces. This may prevent the resulting impregnated rovings 142 frombeing generally uniform. The die and method of the present disclosure,by ensuring that the normal force is less than or equal to the liftforce for rovings traversing contact surfaces 253, cause the rovings 142to not contact the contact surfaces 253 when they are traversing thecontact surfaces 253. Thus, an appropriate amount of resin 214 isrelatively evenly distributed and an appropriate amount of resin 214 isimpregnated, resulting in a generally uniform impregnated roving 142.

As shown in FIG. 18 and discussed above, during impregnation, rovings142 may traverse contact surfaces 252, 253 at angles 254. The rovings142 may further traverse contact surfaces 252, 253 at suitable tensions,as discussed below. Such angle 254 and tension for a particular roving142 and contact surface 252, 253 may be determined at or throughout animpregnation location 302 or portion thereof on the contact surface 252,253. An impregnation location 302 is the location wherein the resin 214and/or roving 142 comes into contact with the contact surface 252, 253for impregnation thereof by the contact surface 252, 253. Animpregnation location 302 in exemplary embodiments may include a peak ofthe contact surface 252, 253. It should be noted that a roving 142traversing a contact surface 253 will not generally contact a contactsurface 253; rather, a portion of the associated resin 214 will remaindisposed therebetween due to the relative relationship between normalforce and lift force.

The normal force of a roving 142 at an impregnation location 302 duringimpregnation may be calculated as a vector component of the tension ofthe roving 142. Such calculation may be made at an impregnation location302 for a contact surface 252, 253, and may be based on the angle 254and tension of a roving 142 at such location. FIG. 19 illustrates oneembodiment of a geometric representation of a roving 142 traversing acontact surface 252, 253 that may be utilized to calculate a normalforce of the roving 142. According to such representation, A representsthe angle 254 at which the roving 142 is traversing a contact surface252, 253, h represents the tension of that roving 142, and a representsthe normal force. The normal force may thus be calculated according tothe following equation:a=sin(A)*h.

It should be understood that calculation of the normal force is notlimited to the above-disclosed equation, and rather that any suitablecalculation of the normal force of a roving 142 traversing a contactsurface 252, 253 is within the scope and spirit of the presentdisclosure.

Further, various other variables may be determined for a roving 142 andassociated resin 214 according to the present disclosure. For example,the speed of a roving 142 as well as the width of the roving 142 at orwithin the impregnation location 302 may be determined. Further, theviscosity of the resin 214 as well as the length of the impregnationlocation 302 and the height of resin 214 within the impregnationlocation 302 may be determined. A porosity factor may additionally bedetermined for the resin. These various factors for a particular roving142 and contact surface 252, 253 may be determined at or throughout animpregnation location 302 or portion thereof on the contact surface 252,253.

The lift force, such as the hydraulic lift force, of resin 214 at animpregnation location 302 during impregnation may be calculatedutilizing the above-determined factors. FIG. 20 is one embodiment of ageometric representation of the interaction between a roving, resin, anda contact surface that may be utilized to calculate a lift force of theresin. According to such representation, η is a viscosity of the resin214 and U is a speed of the roving 142. L is a length of theimpregnation location 302. h is a height of resin 214 within theimpregnation location 302. Such height may be determined at a first endof the impregnation location 302, represented by h_(O), and a second endof the impregnation location 302, represented by h_(L). These heightsmay additionally represent the distance between a roving 142 and acontact surface 252, 253. C is a porosity factor. The porosity factormay be a constant that is estimated or calculated based on the porosityof the resin 214, and may be adjusted as necessary. w is a width of theroving 142. F is the lift force of the resin 214. An equation tocalculate slider bearing pressure may be utilized according to theseembodiments to calculate the lift force, because the interaction of theroving 142, resin 214, and contact surface 252, 253 may be similar tothe interaction between various slider bearing components. The liftforce may thus be calculated according to the following equation:F=(((6ηUL)/h ²)*(((h _(o) −h)*(h−h _(L)))/(h _(o) ² −h _(L) ²)))*C*(w*L)

It should be understood that calculation of the lift force is notlimited to the above-disclosed equation, and rather that any suitablecalculation of the lift force of resin 214 for a roving 142 traversing acontact surface 252, 253 is within the scope and spirit of the presentdisclosure.

It should further be understood that the various determinations ofvariables utilized in the above-disclosed equations may be measured orestimated before or during operation of a die 150 and traversaltherethrough of various rovings 142 and resin 214 to produce impregnatedrovings 142. Further, such measurements or estimates may be made basedon the rovings 142 and resin 214 utilized in the die 150, or may be madebased on general knowledge or information for rovings 142 and/or resin214 having similar characteristics. Still further, the various variablesmay be adjusted as desired or required, and the lift force and/or normalforce thus adjusted, to obtain the desired performance wherein thenormal force is less than or equal to the lift force at an impregnationlocation 302 on a contact surface 253 during impregnation of a roving142 with resin 214 by that contact surface 253.

FIG. 18 illustrates one embodiment of an impregnation zone 250 havingcontact surfaces 253 that allow for the traversal thereof of rovings 142such that the normal force of a roving 142 is less than or equal to thelift force of the associated resin 214 on that roving 142. For example,an impregnation zone 250 may include one or more contact surfaces 253. Acontact surface 253 may be formed on or as part of the first or secondplate 256 and 258. Further, in exemplary embodiments as shown, thecontact surfaces 253 may be located in the downstream portion of theimpregnation zone 250, and may be the final contact surface or contactsurfaces 253 in the run direction 282 of a roving 142. A roving 142being traversed through an impregnation zone 250 according to thepresent disclosure may in exemplary embodiments only encounter contactsurfaces 252 before, and not after, encountering contact surfaces 253.Additionally or alternatively, no contact surfaces 252 in exemplaryembodiments may be disposed downstream in run direction 282 of the finalcontact surface or surfaces 253.

In exemplary embodiments, as further shown in FIGS. 4 and 18, each ofthe contact surfaces 253 for which the normal force is less than orequal to the lift force may be configured such that a roving 142traversing that contact surface 253 is at an angle 254 that is less thanan angle 254 for the remaining contact surfaces 252. Such reduced angle254 for the contact surfaces 253 may reduce the normal force by reducingthe tension in a roving 142 traversing the contact surface 253. Toreduce the angle 254 for a contact surface 253, in some embodiments asshown the height 304 of the contact surface 253 may be reduced. Thus,the height 304 of such contact surface 253 may be less when measuredfrom a common base point than the height of a contact surface 252. Theangle 254 and/or height 304 may be adjusted based on the equations asdiscussed above, or may be otherwise adjusted until the normal force isless than or equal to the lift force or until the impregnation section250 and die 150 produce suitable uniform impregnated rovings 142.

In other embodiments, the angle 254 of a contact surface 253 may bereduced through any other suitable technique, such as by altering theshape of the contact surface 253. Still further, in other embodiments,the contact surface 253 may be adjusted through any other suitabletechnique to reduce the normal force for a roving 142 traversing thatcontact surface 253.

It should be understood that an impregnated roving 142 according to thepresent disclosure may have any suitable cross-sectional shape and/orsize. For example, such roving may have a generally oval or circularcross-sectional shape, or may have a generally rectangular shape orother suitable polygonal or otherwise shape. Further, it should beunderstood that in some embodiments a plurality of impregnated rovings142 having been traversed through the impregnation zone 250 may togetherform a sheet or ribbon, with the resin 214 of the various rovings 142connected to form such ribbon. The various above variables may thus inexemplary embodiments be determined for a single roving 142 or aplurality of impregnated rovings 142, whether connected or separate, asdesired or required.

To further facilitate impregnation of the rovings 142, they may also bekept under tension while present within the die 150, and specificallywithin the impregnation zone 250. The tension may, for example, rangefrom about 5 to about 300 Newtons, in some embodiments from about 50 toabout 250 Newtons, and in some embodiments, from about 100 to about 200Newtons per roving 142 or tow of fibers.

As shown in FIG. 4 and FIGS. 21 and 22, in some embodiments, a land zone280 may be positioned downstream of the impregnation zone 250 in rundirection 282 of the rovings 142. The rovings 142 may traverse throughthe land zone 280 before exiting the die 150. In some embodiments, asshown in FIG. 21, at least a portion of the land zone 280 may have anincreasing cross-sectional profile in run direction 282, such that thearea of the land zone 280 increases. The increasing portion may be thedownstream portion of the land zone 280 to facilitate the rovings 142exiting the die 150. Alternatively, the cross-sectional profile or anyportion thereof may decrease, or may remain constant as shown in FIG.22.

As further shown in FIG. 4, in some embodiments, a faceplate 290 mayadjoin the impregnation zone 250. The faceplate 290 may be positioneddownstream of the impregnation zone 250 and, if included, the land zone280, in the run direction 282. Faceplate 290 is generally configured tometer excess resin 214 from the rovings 142. Thus, apertures in thefaceplate 290, through which the rovings 142 traverse, may be sized suchthat when the rovings 142 are traversed therethrough, the size of theapertures causes excess resin 214 to be removed from the rovings 142.

Additionally, other components may be optionally employed to assist inthe impregnation of the fibers. For example, a “gas jet” assembly may beemployed in certain embodiments to help uniformly spread a roving ofindividual fibers, which may each contain up to as many as 24,000fibers, across the entire width of the merged tow. This helps achieveuniform distribution of strength properties. Such an assembly mayinclude a supply of compressed air or another gas that impinges in agenerally perpendicular fashion on the moving rovings that pass acrossexit ports. The spread rovings may then be introduced into a die forimpregnation, such as described above.

The impregnated rovings that result from use of the die and methodaccording to the present disclosure may have a very low void fraction,which helps enhance their strength. For instance, the void fraction maybe about 3% or less, in some embodiments about 2% or less, in someembodiments about 1% or less, and in some embodiments, about 0.5% orless. The void fraction may be measured using techniques well known tothose skilled in the art. For example, the void fraction may be measuredusing a “resin burn off” test in which samples are placed in an oven(e.g., at 600° C. for 3 hours) to burn out the resin. The mass of theremaining fibers may then be measured to calculate the weight and volumefractions. Such “burn off” testing may be performed in accordance withASTM D 2584-08 to determine the weights of the fibers and the polymermatrix, which may then be used to calculate the “void fraction” based onthe following equations:V _(f)=100*(ρ_(t)−ρ_(c))/ρ_(t)where,

V_(f) is the void fraction as a percentage;

ρ_(c) is the density of the composite as measured using knowntechniques, such as with a liquid or gas pycnometer (e.g., heliumpycnometer);

ρ_(t) is the theoretical density of the composite as is determined bythe following equation:ρ_(t)=1/[W _(f)/ρ_(f) +W _(m)/ρ_(m)]

ρ_(m) is the density of the polymer matrix (e.g., at the appropriatecrystallinity);

ρ_(f) is the density of the fibers;

W_(f) is the weight fraction of the fibers; and

W_(m) is the weight fraction of the polymer matrix.

Alternatively, the void fraction may be determined by chemicallydissolving the resin in accordance with ASTM D 3171-09. The “burn off”and “dissolution” methods are particularly suitable for glass fibers,which are generally resistant to melting and chemical dissolution. Inother cases, however, the void fraction may be indirectly calculatedbased on the densities of the polymer, fibers, and ribbon in accordancewith ASTM D 2734-09 (Method A), where the densities may be determinedASTM D792-08 Method A. Of course, the void fraction can also beestimated using conventional microscopy equipment.

The present disclosure is further directed to a method for impregnatingat least one fiber roving 142 or a plurality of fiber rovings 142 with apolymer resin 214. The method generally includes flowing a polymer resin214 through a manifold assembly 220. The manifold assembly 220 mayinclude a plurality of channels or branched runners 222, as discussedabove. The method further includes coating the fiber rovings 142 withthe resin 214, as discussed above. Further, the method includestraversing the coated roving 142 through an impregnation zone 250 toimpregnate the rovings 142 with the resin 214, as discussed above. Suchtraversing step may include contacting one or more contact surfaces 252and one or more contact surfaces 253, as discussed above. In exemplaryembodiments, as discussed above, at least one contact surface 253 may beconfigured such that a normal force of a roving 142 traversing thecontact surface 253 may be less than or equal to a lift force of theresin 214 on the roving 142 at an impregnation location 302 on thecontact surface 253 during impregnation of the roving 142 with the resin214 by the contact surface 253.

As discussed above, in some embodiments, the step of flowing the resin214 through the manifold assembly 220 may include flowing the resin 214through an outlet region 242 of the manifold assembly 220. As furtherdiscussed above, the step of coating the roving 142 with the resin 214may include flowing the resin 214 from the manifold assembly 220 througha gate passage 270. The method may further include traversing therovings 142 from the impregnation zone 250 through a land zone 280, asdiscussed above. In exemplary embodiments, as discussed above,impregnated rovings 142 exiting the die 150 may be generally uniform.

As discussed above, after exiting the impregnation die 150, theimpregnated rovings 142, or extrudate 152, may be consolidated into theform of a ribbon. The number of rovings employed in each ribbon mayvary. Typically, however, a ribbon will contain from 2 to 20 rovings,and in some embodiments from 2 to 10 rovings, and in some embodiments,from 3 to 5 rovings. In some embodiments, it may be desired that therovings are spaced apart approximately the same distance from each otherwithin the ribbon. Referring to FIG. 23, for example, one embodiment ofa consolidated ribbon 4 is shown that contains three (3) rovings 5spaced equidistant from each other in the −x direction. In otherembodiments, however, it may be desired that the rovings are combined,such that the fibers of the rovings are generally evenly distributedthroughout the ribbon 4. In these embodiments, the rovings may begenerally indistinguishable from each other. Referring to FIG. 24, forexample, one embodiment of a consolidated ribbon 4 is shown thatcontains rovings that are combined such that the fibers are generallyevenly distributed.

A pultrusion process may further be utilized according to the presentdisclosure for certain particular applications. For example, in someembodiments, such process may be utilized to form a rod. In theseembodiments, continuous fibers of rovings 142 may be oriented in thelongitudinal direction (the machine direction “A” of the system ofFIG. 1) to enhance tensile strength. Besides fiber orientation, otheraspects of the pultrusion process may be controlled to achieve thedesired strength. For example, a relatively high percentage ofcontinuous fibers are employed in the consolidated ribbon to provideenhanced strength properties. For instance, continuous fibers typicallyconstitute from about 25 wt. % to about 80 wt. %, in some embodimentsfrom about 30 wt. % to about 75 wt. %, and in some embodiments, fromabout 35 wt. % to about 60 wt. % of the ribbon. Likewise, polymer(s)typically constitute from about 20 wt. % to about 75 wt. %, in someembodiments from about 25 wt. % to about 70 wt. %, and in someembodiments, from about 40 wt. % to about 65 wt. % of the ribbon.

In general, ribbons may be supplied to the pultrusion system directlyfrom impregnation die 150, or may be supplied from spindles or othersuitable storage apparatus. A tension-regulating device may be employedto help control the degree of tension in the ribbons as they are drawnthrough the pultrusion system. An oven may be supplied in the device forheating the ribbons. The ribbons may then be provided to a consolidationdie, which may operate to compress the ribbons together into a preform,and to align and form the initial shape of the desired product, such asa rod. If desired, a second die (e.g., calibration die) may also beemployed that compresses the preform into a final shape. Cooling systemsmay additionally be incorporated between the dies and/or after eitherdie. A downstream pulling device may be positioned to pull productsthrough the system.

These and other modifications and variations of the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention so further described in such appended claims.

What is claimed is:
 1. A method for impregnating at least one fiberroving with a polymer resin, the method comprising: flowing a polymerresin through a manifold assembly of a die, the manifold assemblycomprising a plurality of branched runners; coating at least one fiberroving with the resin; and traversing the coated roving through animpregnation zone of the die to impregnate the roving with the resin,the impregnation zone comprising a plurality of contact surfaces,wherein a normal force of the roving is less than or equal to a liftforce of the resin at an impregnation location on at least one of theplurality of contact surfaces during impregnation of the roving with theresin by the at least one of the plurality of contact surfaces.
 2. Themethod of claim 1, wherein the at least one of the plurality of contactsurfaces is a final contact surface in a run direction of the roving. 3.The method of claim 1, wherein no contact occurs between the roving andthe at least one of the plurality of contact surfaces duringimpregnation of the roving with the resin by the contact surface.
 4. Themethod of claim 1, wherein the impregnation location comprises a peak ofthe contact surface.
 5. The method of claim 1, wherein the normal forceis calculated using the equation:a=sin(A)*h wherein a is the normal force, A is an angle at which theroving traverses the at least one of the plurality of contact surfaces,and his a tension of the roving.
 6. The method of claim 1, wherein thelift force is calculated using the equation:F=(((6ηUL)/h ²)*(((h _(o) −h)*(h−h _(L)))/(h _(o) ² −h _(L) ²)))*C*(w*L)wherein F is the lift force, η is a viscosity of the resin, U is a speedof the roving, L is a length of the impregnation location, h is a heightof resin within the impregnation location, C is a porosity factor, and wis a width of the roving.
 7. The method of claim 1, wherein each of theplurality of contact surfaces is configured such that the rovingtraverses the contact surface at an angle in the range between 1 degreeand 30 degrees.
 8. The method of claim 1, wherein the at least one ofthe plurality of contact surfaces is configured such that the rovingtraverses the at least one of the plurality of contact surfaces at anangle that is less than the angle of the remainder of the plurality ofcontact surfaces.
 9. The method of claim 1, wherein each of theplurality of contact surfaces comprises a curvilinear contact surface.